Comparison of Pelvic Alignment among Never-Pregnant Women, Pregnant Women and Postpartum Women (Pelvic Alignment and Pregnancy)

Objective: To compare the pelvic alignment among never-pregnant women, pregnant women, and postpartum women. Methods: A total of 177 nulliparous women (mean age, 18.9 ± 1.0 years), 45 pregnant women between the third and tenth month of pregnancy (mean age, 29.4 ± 3.8 years), and 124 primiparous women between the first and sixth months after delivery (mean age, 30.1 ± 4.4 years) were enrolled in this study. Pelvic alignment was measured by using the anterior superior iliac spine (ASIS) and posterior superior iliac spines (PSIS) as landmarks. The bilateral difference of pelvic tilt was defined as pelvic asymmetry (PA), the distance between bilateral ASIS was defined as the anterior width of the pelvis (AWP), and the distance between the bilateral PSIS was defined as the posterior width of the pelvis (PWP). Results: PA of the pregnant group and postpartum group were significantly greater than the never-pregnant group (2.8 ± 2.4°, 4.2 ± 3.0°, and 3.7 ± 3.2°, respectively, p < 0.001). AWP of the pregnant and postpartum group was wider than the never-pregnant group (24.9 ± 0.3 cm, 24.1 ± 0.1 cm, and 23.6 ± 0.2 cm, respectively, p < 0.001). PWP of the pregnant and postpartum group was narrower than the never-pregnant group (8.2 ± 0.3 cm, 8.6 ± 0.1 cm, and 9.2 ± 0.1 cm, respectively, p = 0.008). In the multivariate regression analysis using never-pregnant women as the reference, pregnant and postpartum women were significantly more likely to have greater PA (β = 0.156, 0.156), wider AWP (β = 0.116, 0.202), and narrower PWP (β = -0.132, -0.147) than never-pregnant women. Conclusions: We found that the alignment of the pelvis was different among never-pregnant, pregnant, and postpartum women.